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world now emits more than 30 billion tons of
CO each year. Meanwhile, natural processes
that could counter acidi cation---such as the
weathering of rocks on land---operate far too
slowly to make a di erence on a human time-
scale. Even if CO emissions were somehow to
cease today, it would take tens of thousands of
years for ocean chemistry to return to its pre-
industrial condition.
Acidi cation has myriad e ects. By favoring
some marine microbes over others, it is likely
to alter the availability of key nutrients like iron
and nitrogen. For similar reasons it may let more
sunlight penetrate the sea surface. By changing
the basic chemistry of seawater, acidi cation
is also expected to reduce the water's ability to
absorb and mu e low-frequency sound by up
to 40 percent, making some parts of the ocean
noisier. Finally, acidi cation interferes with re-
production in some species and with the abil-
ity of others---the so-called calci ers---to form
shells and stony skeletons of calcium carbonate.
ese last e ects are the best documented ones,
but whether they will prove the most signi cant
in the long run is unclear.
In 2008 a group of more than 150 leading
researchers issued a declaration stating that they
were "deeply concerned by recent, rapid changes
in ocean chemistry," which could within decades
"severely a ect marine organisms, food webs,
biodiversity, and sheries." Warm-water coral
reefs are the prime worry. But because carbon
dioxide dissolves more readily in cold water, the
impact may actually show up rst closer to the
Poles. Scientists have already documented sig-
ni cant e ects on pteropods---tiny swimming
snails that are an important food for sh, whales,
and birds in both the Arctic and the Antarctic.
Experiments show that pteropod shells grow
more slowly in acidi ed seawater.
Will organisms be able to adapt to the new
ocean chemistry? e evidence from Castello
Aragonese is not encouraging. The volcanic
vents have been pouring CO into the water
for at least a thousand years, Hall-Spencer told
me when I visited. But the area where the pH is
7.8---the level that may be reached oceanwide by
the end of the century---is missing nearly a third
of the species that live nearby, outside the vent
system. ose species have had "generations on